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Lemming Population Flux Solved: Mass Suicide Not to Blame
quogmire writes "Australia's ABC reports that biologists from the Universities of Finland and Freiburg (Germany) have finally solved the question of lemming population fluctuations once thought to be caused by lemmings mass-suiciding by plunging off cliffs. 'Lemming populations, they say, surge spectacularly and fall just as quickly, thanks to the combined feasting of four predators: the stoat, arctic fox, snowy owl and a seabird called the long-tailed skua.' The original article (Login required) is published in Science."
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well, at least now I know that its just not God pushing the mushroom cloud button!
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because I keep clicking the bomb icon and blowing them up?
Why study Lemmings when you can study Pingus?
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I thought it was because I should have had one build that bridge across the chasm. I didn't consider that the game had predators as well.
What? There are STILL people that believe that lemmings mass suicide?! Geez, what a hoax.
It's well known, by me at least, that the whole 'lemming suicide' thing was something that Disney cooked up during their 'bad documentary' era. In this case the lemmings were hearded off a cliff by the documentary crew, and was filmed as a 'mass suicide'.
I've seen some pretty amusing/sad documentaries that came out of Disney, including one that had the antics of a Jaguar eating various creatrues. It was OBVIOUS that it was a jaguar in a rather well done habitat where they threw in various animals, mostly eels, for the jaguar to attack. It was exceptionally amusing, but sad, too, that they thought to do something like this and pass it off as truth.
those Disney lemmings didn't commit suicide, they were MURDERED! *gasp*
So is the old Psygnosis game now obsolete and environmentally incorrect?
They're not suicidal, they're just tasty!
"I only speak the truth"
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This doesn't concur with the results I got from my private investigations regarding the behaviour of lemmings. I did some massive computer simulations during the 90's, which showed that lemmings are stupid animals which will walk into one direction until they fall off the cliff. Only few of them can use jack-hammers or parachutes, and even that not without explicit order.
*puts hands on head* Oh-no!!!
*POP*
I guess whoever did this study failed their first ecology course in college.
Almost every ecology teacher beats several key things into your heads.
1. Survival of the fittest
in other words an individual does not do something for the benifit of the species, mainly due to the fact that doing so diverts energy that could be used to producing more young so that their genes survive. The individual will do things to benifit their genes, but not for unrelated individuals of the same species. Social species do have some altruistic behaviours, but their communities are generally made up of individuals that are related. However these altruistic behaviors do not include suicide.
2. The lynx and Hare.
Classic example of what is going on with the lemmings here. As the hare population increases there is more food for the lynx, thus more offspring are produced. As the lynx population increases there are fewer hare to eat and the lynx population declines, and so on.
So this study on lemmings is not surprising, actually I'm quite shocked that someone didn't figure it out sooner.
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Apparently it has also been found that when the lemmings do jump off the cliff, they all have little umbrellas to make it down safely.
But I just wanted to point out that the ABC article is somewhat misleading. The original research article at no point addresses or attempts to refute the mass-suicide myth. Because, honestly, no scientist believed that was possible. The question they considered was much more reasonable: do the large deviations come from predators eating lemmings, or from a lack of vegatation for the lemmings to eat? It seems as though they have resolved that the crashes in population come from predator over-population, not from food scarcity.
This article will probably not shake the foundations of population dynamics. As some other posters have pointed out, it is not so surprising that one sees immense highs and massive crashes in a predator-prey system, because these phenomena exist even in simple mathematical models of pred-prey systems. So for a mathematician this should fly right under the radar.
On the other hand, to a population dynamics guy, this is somewhat interesting, as in that field it is typically considered hard to model these dynamics accurately. It seems as though these guys have determined some parameters in the population dynamics model experimentally, and this is what it is interesting.
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Apart from the "University of Finland" and all the cutesy Lemmings jokes, does this strike anyone as horrificly unscientific? I mean, it's been observed for ages that the growth of the population of the prey causes a growth in population of the predator. Then your population growth for the lemmings looks something like:
dL/dt = bL/2 - hP
where L is the lemming population, b is the average number of lemmings born in a time interval, P is the number of predators and h is some constant. P on the other hand is related to L by some observed relation:
dP/dt ~ L
Given suitable values for b and h we can predict the behaviour of the lemming population without having to invent catastrophic events to explain the fluctuations of L without any empirical evidence to support them.
For example, if you assume that the population is governed by a continuous-time model, i.e. by a differential equation, then it is not really possible for a population to exceed a carrying capacity, and then crash. What happens is that the population asymptotically approaches the carrying capacity, but can never go above it. I think it is reasonable to put humans in this case, as our growth rate is a smooth frunction of time (no breeding season, for example).
Aside note: for those who may not know, the term "carrying capacity" is a term used in population dynamics which sort of represents the available resources. In most models, what happens is that there is some amount of population which can be supported by the existing resources, and if the population is below that, it should grow, and above that, it should shrink. Most "reasonable" models of population dynamics have such a carrying capacity, and I can even state a theorem: if you have any model where the growth rate of a species depends on its size, AND it is true that this growth rate becomes negative for some sufficiently large value of the population, then you will have a carrying capacity. Furthermore, if nothing in the system changes, the population will approach this value and stay there forever.
Now, I'm not saying a crash is impossible, but you need a more complicated system. There are several ways to add complexity to the system. One way is to consider a predator-prey type of system, but of course humans have nothing which can really be called a predator. The only thing I can think of is some sort of disease, but this leads to a different model altogether (some sort of "epidemological model"), and these models rarely predict population crashes, as they have a different character, which is disease needs to be carried by disease-carrying individuals (ok, duh) but then these tend to die out. So the predator carries its own destruction around with it, in some sense, and it corrects itself.
Another postulate one can make, and I think this is somewhat reasonable, is that the carrying capacity of the earth might change radically in the future (and of course, radically downward would be the interesting case in this discussion). This could happen any number of ways. And if it turns out that the carrying capacity moves on some very quick timescale (much more rapid than the change in growth of the population), then we could see a "crash". For example, if it turned out that our ability to grow food took a big hit for some reason or another, then this could happen.
One last way to get population crashes is to consider the case of the discrete system. For example, this does apply to species which have a discrete (say, yearly) breeding system. The population does not change smoothly over time, but is simply a function of one year to the next. It is somewhat surprising, but true, that the dynamics of a population with a discrete model can be much more complicated than those with a continuous model. In fact, a discrete model can actually have what satisfies the mathematical definition of "chaos". Thus you can see any type of behaviour you might imagine, including crashes, but also including periodicity (say, a 17-year cycle for population values). I do not think it is reasonable to assume that humanity can be modeled by this sort of model, even in a coarse-grained sense, because we breed day in and day out all the time. This (and this is somewhat surprising) makes our population a much more stable quantity.
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A popular survival strategy for many insects is to synchronize their breeding so that they produce a huge number of offspring within a short period of time. The predators can stuff themselves silly but there are plenty of survivors.
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